Boregrinding is an operation in which excess internal stock is removed from a tubular workpiece. This process generally involves clamping the tubular workpiece on a boregrinding machine, and then operating on that clamped workpiece.
In the past, workpieces have generally been clamped by jaws that are engaged against the outer surface of the workpiece while being attached to the boregrinding chuck. The jaws can be machined to size or manufactured to size. If the jaws are to be used on a plurality of different sized workpieces, they must be cut to size each time.
This procedure causes many problems. First, the machinist must estimate the size of the jaw that will be required, and then remove the proper amount of material from the existing jaw. In the present environment that requires extremely accurate machining of bores, especially in the ball bearing art, such estimation is simply not precise and accurate enough. Jaws machined in this manner may create non-circular and deformed workpieces. At the least, such jaws might produce a workpiece that is out of tolerance limits at least in some areas of its perimeter.
Second, the prior jaws used in the boregrinding field have contacted the workpiece at a small area, nearly point contact in fact. Such point contact has created problems known as "six point" in which the workpiece is deformed by contact with the point sized jaw. At the very least, such point contact may produce a deformed, non-circular outer perimeter for the workpiece.
It is noted that this point contact has created other problems as well as the above-mentioned problems when determining how much "pinch" must be used. "Pinch" is defined as that amount of size difference required between the jaws inner diameter and the outer diameter of the workpiece so that there is sufficient frictional engagement between the jaws and the workpiece to hold that workpiece securely enough to perform the boregrinding operation. To illustrate, if the outer diameter of the workpiece is 2", a pinch of 1/64" will cause the inner diameter of the jaws to be (2"-1/128") so that the workpiece-engaging circle defined by the inner, workpiece-engaging surface of the jaws will be less than 2" in diameter. This smaller diameter will "pinch" the workpiece and thus hold it in position during the boregrinding operation.
However, if the contact between the jaws and the workpiece is of a small area, i.e., a point contact, the pinch must be extremely high since the force applied to the workpiece is a function of the area of contact, and such area is small for the point contact. This high pinch tends to exacerbate the deforming influences of the jaws even more than the point contact itself. Thus, the point contact elements of the prior art tend to cause a deformation of the workpiece for several reasons.
Accordingly, there is a need for a boregrinding chuck assembly which includes jaws that can be customized to precise and accurate sizes and which will not tend to deform the outer perimeter of the workpiece during a boregrinding operation.
Still further, in addition to the above-discussed shortcomings, the prior art boregrinding jaws are not amenable to easy and expeditious customizing. Therefore, there is a further need for a boregrinding chuck assembly that can be easily and expeditiously customized while still overcoming the above-discussed problems associated with the prior art.